Sorting among school teachers, whereby high-qualified school teachers often teach high-achieving students, is well documented, but relatively little is known about how this sorting arises. Based on Danish administrative records, we formulate and estimate a semi-structural dynamic model of career choice among 10 cohorts of teachers completing teacher college, whom we follow biannually up to 15 years. Among teachers initially in the public school, dynamic sorting results in high-qualified teachers moving towards teaching in high-achieving public schools or private schools, while the least-qualified teachers enter low-SES public schools and stay there. Teachers leaving the public or private school system are found to have certain time-constant unobserved characteristics that either immediately or over time make them choose other occupations.